1. Field of the Invention
The invention relates generally to a device used for the testing of physical, chemical, biological or biochemical properties, characteristics, or reactions. More particularly, the invention is directed to an assay plate having an array of raised pads or plateaus for receiving samples thereon.
2. Description of Related Art
Assay plates, otherwise know as assay trays, sample trays, microtiter plates, microplates, well plates, or multi-well test plates, are well known in the art. These assay plates are generally used for chemical or biological experiments, such as the parallel detection and monitoring of biological or chemical reactions, cell growth, virus isolation, titration, toxicity tests, characterization testing, crystallization, or combinatorial synthesis or testing of reactants.
Over the years, many assay plate geometries have been developed to hold samples during such chemical or biological experiments. Most of these assay plate geometries, however, generally include an array or matrix of small sample holding cavities, indentations, or wells.
However, these assay plates with cavities or wells have a number of drawbacks. For example, organic solvent-based fluids tend to wick up the sides of the wells, thereby coating the side walls, changing the geometry of the fluid volume (surface area, pathlength), or causing the fluid to come out of the cavity. Also, the walls defining the wells, although often transparent, interfere with viewing the samples in the wells. Furthermore, the well walls create an impedance for analytical probes getting close to or contacting the sample in the wells. Still further, because these assay plates are often reused, they are cleaned or washed between uses to avoid contamination. However, complete removal of the samples from the wells is typically problematic, as it can be more difficult to clean out all the wells of a well plate, especially if the wells have tight corners or contain a sample that is dried or resistant to cleaning. In this case, mechanical “scrubbing” is required and efficient and complete scrubbing is hindered by the presence of walls.
Another type of assay plate developed by the Discovery Labware business unit of BD Biosciences (Becton, Dickinson and Company) is the BD FALCON™ virtual-well plate. The BD FALCON™ virtual-well plate is used to create an array of aqueous-based liquid samples by tailoring the surface-tension properties of a substrate to achieve sample separation without wall features, such as wells. These virtual-well plates consist of a hydrophilic substrate coated with a hydrophobic mask layer containing an array of openings or virtual-wells that are left uncoated. A sample liquid is deposited into each uncoated hydrophilic virtual-well. As each virtual-well is surrounded by the hydrophobic mask, high contact angles are created where the sample liquid contacts the mask, thereby restricting fluid transfer between the virtual-wells.
These virtual-wells work sufficiently well for aqueous-based sample liquids with high surface tensions. However, when low surface tension fluids, such as organic solvent-based fluids or surfactants containing aqueous samples, are used on these virtual-well plates, the sample liquid is not sufficiently contained within the virtual wells. This leads to adjacent drops merging with one another, thereby impairing the value of the plate.
In light of the above, there is a need for an improved assay plate that can hold multiple samples, while addressing the drawbacks of the prior art. Specifically, the assay plate should be able to define an array of distinct samples. In addition, the assay plate should be capable of being used with any type of liquid, including organic solvent-based liquids, while providing unobstructed views and/or contact with each sample thereon.